The invention concerns a handleable working device, in particular a pressing device, having a tool, in particular a pressing tool; an electric motor for driving the tool; a battery, in particular rechargeable, for supplying energy to the electric motor; and having a control device which has a voltage comparison element that performs a voltage comparison between the present battery voltage and a limit voltage, such that the control device generates an attention signal and/or limits activation of the electric motor so as to spare the battery if the voltage comparison indicates that the present battery voltage is equal to or less than the limit voltage.
For assembly purposes or for processing purposes, handleable working devices that substantially comprise a tool and an electric motor for driving the tool are known. For joining pipes, for example, pressing devices are used with which a press fitting, which is slid over the pipe ends in order to create the pipe join, is radially compressed. Pressing devices of this kind are known, for example, from EP-A-0 627 273. Handleable working devices of fundamentally the same design, as is evident for example from EP-A-0 676 835, are also used to install cable lugs onto cable ends. The electric motor need not act directly on the tool. Its energy can also be converted into a hydraulic drive system which then acts on the tool.
As EP-A-0 676 835 further shows, energy can also be supplied to the electric motor via a replaceable and also rechargeable battery, so that the working device can be used even in places where no electrical power system exists. With such battery-driven devices, it is important to know whether the energy content still available in the battery is sufficient to perform a further operation (in the case of a pressing tool, a further pressing cycle). In modem batteries based on nickel-cadmium or nickel-metal hydride, the residual energy content is difficult to observe, since these batteries have a characteristic curve with an almost constant voltage level over a long period, the voltage decreasing relatively steeply only toward the end. The result of this can be that one working cycle still proceeds entirely normally, while the subsequent working cycle cannot be completed because the battery is discharged.
In EP-A-0 676 835, it is proposed to equip the working devicexe2x80x94in this case a cable lug crimping devicexe2x80x94with a voltage measurement device to sense the particular battery voltage, and with a voltage comparison element having at least one memory for at least one limit voltage. The voltage comparison element is activated before the electric motor is switched on, and performs a voltage comparison between the present battery voltage and the limit voltage. If the voltage comparison indicates that the present battery voltage is equal to or less than the limit voltage, the electric motor is not started. At the same time, a visual indication is given. EP-A-0 676 835 contains no information as to how the battery voltage is measured.
It is the object of the invention to configure a working device of the kind cited initially in such a way that working cycles are started only if sufficient battery capacity is still present for the working cycle in question.
According to the present invention, this object is achieved in that the control device has an interval element with at least one stored interval; and that a load element is present by way of which the battery can be acted upon by a load cycle that generates a voltage curve with a varying battery voltage, the interval element being activated at least once after the load element is switched on, and the voltage comparison being performed within the interval.
The basic idea of the invention is consequently to act upon the battery with a load cycle that generates a voltage curve with a changing battery voltage, and then to perform the voltage comparison within at least one interval having a characteristic voltage curve. If the voltage remains below a limit voltage within the interval, an attention signal is generated, for example an electrical or audible alarm, and/or activation of the electric motor is limited or the electric motor is immediately inhibited, so that complete discharge of the battery does not occur.
The load element can be the electric motor itself, i.e. in this case the electric motor is switched on, and the voltage comparison is performed within at least one interval having a characteristic voltage curve. The load element can instead also be an adjustable resistor in the form of a potentiometer, with which the load cycle is generated. This version is advantageous if the battery is separate from the working device and is joined to it only via a cable. In this case the charge state of the battery can be checked independently of the working device and thus also without any connection to it, if the corresponding circuit is arranged in the housing for the battery. The two types of circuit can, however, also be combined with one another, by the fact that the resistor is arranged electrically in parallel with the electric motor and by way of a two-way switch either the resistor or the electric motor is selectably switched in as the load element.
In a particularly advantageous embodiment of the invention, it is proposed that the is voltage comparison element be configured as an analog comparator to which the battery voltage on the one hand and the limit voltage on the other hand are applied. The limit voltage can be generated by an auxiliary battery. The comparator switches logic states if the present battery voltage either exceeds or falls below the limit voltage. The circuit described above requires no current measurement system or parts that define current measurements, and is thus notable for its simplicity. In the case in which the load element is the electric motor itself, the voltage comparison places no load on the battery.
The interval element is preferably configured as a timing element. The interval can instead also be defined in a different manner, for example by sensing a specific number of revolutions of the electric motor or the like.
In one embodiment, the interval element is activated as the load element is switched on, i.e. the interval begins with actuation of the load element. Alternatively, there also exists the possibility that the voltage comparison element performs a voltage comparison after the load element is switched on, and the interval element is activated only when it is determined that the present battery voltage has reached, or falls below or exceeds, a second limit voltage. In this context, the first and the second limit voltage are preferably identical.
The load element should produce a start-up phase with a voltage drop, and then a subsequent voltage recovery, as is the case in most situations (in particular with pressing devices) when the electric motor is the load element. The voltage drop results from the high current consumption caused by the fact that the parts driven by the electric motor must be accelerated to its idle speed. In this case the interval element should be activated in such a way that the interval lies within the start-up phase.
If the interval lies within a phase of a very pronounced voltage change, for example within the start-up phase described above, the activation of one interval is sufficient to obtain a reliable indication as to the charge state of the battery and to take countermeasures if the risk exists that the battery charge is no longer sufficient for the present or future load cycle. An improvement can be achieved in this context, however, by the fact that the interval element is activated more than once, at separate times, within the load cycle; here again, it is advantageous to activate the interval element only in regions of the load cycle where a voltage drop and a subsequent voltage recovery take place. Alternatively, however, provision can be made for the intervals to be directly adjacent to one another at least over a portion of the load cycle, preferably over the entire load cycle, so that a continuous voltage comparison as defined above takes place. Both versions are advisable in particular when different limit voltages are associated with the intervals, so that the voltage curve can be tracked and analyzed even with greatly fluctuating voltages. If a comparator is used for the voltage comparison element, provision can be made to apply to the comparator different limit voltages that are switched in alternatingly. An adjusting element with which the limit voltage supplied for each interval can be set differently can also, however, be present. It is understood that this is accomplished by way of a corresponding circuit before the interval or as it begins.
Regardless of whether only one interval or several intervals is or are activated for the voltage comparison, provision is furthermore made according to the invention for the limit voltage(s) to be modifiable, for example in order to adapt it/them to altered conditions such as temperature or aging of the moving parts of the working device. A temperature measurement device can be provided, for example, such that the lower the temperature, the higher the setting, within a design temperature range, of the limit voltage associated with the respective interval and/or the shorter the length of the interval or intervals. This takes into account the circumstance that the energy content of a battery is less at lower operating temperatures than at higher temperatures. In addition, provision should be made for the limit voltage(s) to be elevated, by the action of the temperature measurement device, if the temperature sensed by the temperature measurement device lies above or below the design temperature range. If the limit voltage(s) is or are sufficiently high, this prevents the working device from being put into service at temperatures that are damaging to the battery. It is particularly advantageous if the temperature measurement device directly measures the temperature of the battery, since in this fashion it is possible to take into consideration the heating of the battery immediately once the electric motor is started, so that the limit voltage(s) can be decreased.
In a further embodiment of the invention, provision is made that in one load cycle, at least one present battery voltage is stored; and that a comparison is made, in a load cycle subsequent thereto, between the previously stored battery voltage and the present battery voltage in the same phase of the load cycle, a higher limit value or higher limit values being utilized, and/or the length of the interval or intervals being shortened, if the present battery voltage is lower than the stored voltage. This makes it possible to take into account gradual changes, especially those due to aging processes, so that even in such cases it is possible reliably to prevent the working device from being put into service if the charge state of the battery no longer allows for further working cycles. The comparison should preferably be made in a phase of constant load generation by the load element, since the gradual changes are most easily detectable there.
Provision is furthermore made according to the invention for the tool to be returned to the starting position by the electric motor if the voltage comparison indicates that the present battery voltage is equal to or less than the limit voltage. The remaining charge in the battery is thus used to reach the starting position and thus to release the workpiece. This type of utilization of the remaining energy also occurs if a visible or audible indication is given. In addition, the electric motor should be shut off, immediately or after the tool has returned to the starting position (and in fact inhibited in the latter case), if the voltage comparison indicates that the present battery voltage is equal to or less than the limit voltage.
Alternatively, provision can be made for the load cycle to be carried to completion if the voltage comparison indicates that the present battery voltage is equal to or less than the limit voltage, and for the electric motor to be inhibited until the battery is replaced. Provision can also be made, however, for the electric motor to be inhibited only after a limited number of load cycles, until the battery is replaced.